Electron emission material and method of manufacture



Patented'July 6, 1926.

UNITED STATES PATENT OFFICE.

:oml WY MABDEN, OF EAST ORANGE, NEW JERSEY, ASSIGNOB. TO WESTING- HOUSE LAM]? COMPANY, A PENNSYLVANIA CORPORATION.

mOTBON EMISSION MATERIAL AND METHOD OF MANUFACTURE.

Io Drawing.

This invention relates to electron-emission material and more particularly to that composed of alkaline-earths made conductive by the admixture therewith of linelydivided metallic material.

An object of my invention is the manufacture of electron-emission material in which the active electron-emitter is a refractory oxide, substantially non-conductive and having conductivity imparted thereto by the incorporation therewith of conductive material, for example, metallic powder.

Another object of my invention is the production of electron-emitting material consis of alkaline-earths impregnated with metal 'c material to make them conduct electric current cohere firmly in the desired form and adhere more firmly to a metallic core, if such is'used, with less cracking oil in use, whereby the life of such material ma be increased.

1 further object of my invention is the formation of filamentary material provided with a thicker coating of electron-emitting oxides than heretofore, without impairing the electron-emissivity of the material.

A still further object of my invention is the manufacture of composite wire consisting of metal impregnated with alkaline earths to make it emit electrons efliciently when heated and which may, if desired, be provided with a metal core.

Other vtzlbfleets and advantages of the invention be disclosed from the followin detailed description.

e alkaline earths, that is, the oxides of barium, strontium and calcium have been found to be excellent material for electronemission purposes when heated to proper temperatures. Barium oxide has been found to have the highest electron-emissivity of the three but is usually mixed with strontium oxide for mechanical reasons, that is, the mixture of the two oxides is found to adhere to filamentary material better than barium oxide alone. A common method of m use of the'electron-emitting properties said oxides is to coat platinum-iridium ribbon with a mixture of the oxides of barium and strontium and introduce the same into an electron device as the hot cathode thereof.

It has been found that'only a very thin coating can be applied to a ribbon or filament or this purpose, because of the non- Appllcation filed September 28, 1922. SerlalNb. 591,157.

conducting properties of such oxides. When used in such electron device, the small amount the oxide on the filament gradually vaporizes and the filament finally develops hare spots or portions from which the oxide has been completely vaporized, thus causing a diminution of the electron-emissivity of such coated filament as well as other undesirable consequences. It the oxide is applied thicker than usually, the electron-emissivity of the filament is reduced because of the insulating properties of the oxide.

According to my invention, I obviate the above noted difliculties by mixing a finely divided conductive material with the oxide material.

Another embodiment of my invention involves the making of the filament entirely of electron-emitting oxides impregnated or intimatelymixed with conductive material. Such conductive material is preferabl one of the refractory metals, such as platmum,

tantalum or the like, but other metals are contemplated for use in this connection, for example, chromium, iron, nickel and the like.

Essentially, my invention comprises intimately mixing and incorporating together powdered alkaline earths, for example, a mixture of the oxides of barium and strontium or the carbonates thereof, which may readily be decomposed to form. the oxides, with finely divided or powdered platinum, tantalum or the like. Instead of using platinum, a platinum compound, such as platinic chloride, mixed with reducing agent, such as paste, may be used.

The mixture may then be made into the form of a suspension and applied to any desired filamentary material by any suitable known method; for example, it may be mixed with a suitable binder, such as nitrocellulose dissolved in amyLacetate, applied to filamentary material, such as tantalum or platinum-iridium ribbon, by assing the same through said suspension, an baking the same onto the filament in the same way, as is described, for example, in the copending application of Marden and Rentschler, Serial No. 489,108, filed August 1, 1921, composite bodies and method of producin the same and assigned to the Westing ouse Lamp Company.

The mixture of oxides and metal may be made up as an aqueous suspension, if desired, and the platinum-iridium or other heated to cause it to bake firmly thereto.

Suchrocedure is similar to the method describe and claimed in the copending application of' MacRae and Richardson, Serial No. 566 7, filed June 8, 1922, getters and the app cation thereof and assigned to the Westinghouse Lamp Company. The method iiescribed faqgi claimeill in Rthe co app ication o uncan ac ae, SerH fi' O 587,270, filed September 11, 1922 electron emitting devices and method of making and assigned to the Westinghouse Lamp Company, may be used for coating filamentary material with a mixture of alkaline-earth carbonates and powdered metal, such carbonate being eventually reduced to oxide according to the method disclosed in said application. 1

Instead of coatin filamentary material 4 with such mixture, t e same may be formed into a thick paste and squirted into a filament in a manner similar to that in which swaged or rolled down by suitable known pr and finally drawn to wire of the dedred size by which method there would be obtained an oxide-impregnated filament having an electron-emissivity corresponding with that of the alkaline-earths emfollowing description is given to illustrate more clearly how my invention may be practiced, but it is to be understood that the. pro rtionsgiven are merely suggestive and I not intend to be bound thereby.

'Filamentary material, for example, platinum-iridium ribbon, ma be thoroughly cleaned, as by passing it t rough an electric tube furnace, according to the method described in the aforementioned copending application of-Duncan MacRae. A sus nsion of preferably about equal parts 0 the oxides ofbarium and strontium with any desired pro rtion ofmetal powder, for example, lfiilatmum powder, tantalum powder or the e, may be prepared. a

The vehicle used for such a suspension is preferably water, but an organic binder such as nitro-cellulose dissolved in amyl-acetate may be used if desired. The proportion of the metal owder to the alkaline earths depends on t e thickness of coating to be applied to the filamentary material and may vary from a small amount, for example, form 5 to to a relatively large pro ortion vfor example, from to e thicker the'coatmg to be applied to the filamay be applied to the filamentaix.

the metals themse mentary material, the lar er the proportion of metal powder should in the mixture.

The mixture may be ground up in a mortar with a pestle and enough water gradually added to form a homogeneous suspens1on having the consistency of a thin paste.

Such a suspension may be oured into a gettering cup or the like and t e filamentary material passed over or around the gettermg wheel thereof to coat the same uniformly with the suspension, after which the lib ament may be passed through an electric furnace where the suspension is baked thereon, similar to the method described and claimed in the aforementioned application of Duncan MacRae for applying alkalineearth carbonates to a filament.

One or more coatings of the suspension material, depending on the thickness of e coatin desired thereon. Filamentary materi coated as aforedescribed, 'ts the use of a thicker coating than if no metal were mixed with electron-emitting oxides, because the metal powder in the coatin serves as a conducting medium to bring the electrons to the surface, the electron-emitting oxide serving merely as the final gate-way b means 0 which the electrons are disc arged. Such coated material has a longer life than previously prepared oxide-coated filaments, ecause of the thicker coating of the oxide thereon, whereby the same may be heated for a longer time before all the oxide is completely vaporized from any portion of the surface of the original filament or metallic core of the coated filament, Such a art metallic coating will adhere more firml y to a wire than one containing no free metal.

Another embodiment of my invention comprises utilizing such sus nsion as -is heretofore described for ma g squirted filaments. Of course, in this case, it is necessary to use less of the vehicle, so that a suspension of a consistency of a very thick paste is formed. If water is used for the vehicle, it is preferable to use some binder, such as glue, ut any suitable vehicle may be used so that a squirted filament of suflicient stregfth for the necessary handling is prepar Platinum or tantalum powder are preferably mixed with a relatively small proportion of the oxides of barium and strontium, or the oxide of barium only, so that the squirted filament, when sintered, will have substantially the physical characteristics of ves. Instead of squirting a filament from such a mixture, platinum or tantalum powder may be mixed with a small proportion of one or more 'of the alkaline earths, pressed into a slug and sintered, swaged or rolled and drawn to wire of the desired size, according to well lmown methods now employed in the manufacture of metals of the tungsten class into filamentary form.

.It will readily be appreciated that, according to my invention, I have devised a way for activating filamentary material with alkaline earths in a manner involving the use of said earths in greater thickn than have heretofore been feasible, whereby greaetsr efliciency and longer life are obtain 'Altliou h I have described what, at resent, consider to be the preferred emiments of my inventive idea, it is to be understoodthat modifications will sugfifiastu.

themselves to those skilled in the art w the spirit and scope of the appended claims and that such modifications are to be.considered as embodying my invention.

What is claimed is: 1. Electron-emission material co prism an alkaline earth uniformly distributed thr h tantalum.

2. lectron-emission material'in coherent form com rising alkaline earths uniformly distributed through tantalum.

. 3. Filamentary material for electron-emission pur oses comprising a mixture of the oxides o barium and strontium made conductive by having powdered tantalum metal uniformly distributed therethrough and incorporated therewith.

4. Electron-emission material comprising a conductive core, coated with a non-conductive oxide impre ated with tantalum.

5. Electron-emission material comprising a conductive filament having a coating thereon of alkaline earths mixed with 6. Electron-emission material comprising a filamentary metal core coated with a mixtantalum metal and working the same into the desired coherent form.

9. The method of making filamentary material for electron-emission purposes, comprising uniformly mixing together finely divided tantalum and a small proportion of at least one of the alkaline earths and workling said material into coherent filamentary orm. 10. The method of manufacturing filamentary material for electron-emission purposes compnsing preparin the oxides of arium an strontium and finely divided tantalum metal uniformly distributed therethrough, passing a refractory metal filament through said suspension to coat the same therewith and heating said filament to cause a firm adherence of the,

mixture thereto.

11. The method of manufacturing filamentary material for electron-emission purposes, comprising coating tantalum wire with a uniform mixture of metallic tantalum and alkaline earth material.

In testimony whereof, I have hereunto subscribed my name this 27th day of Sept, 1922.

JOHN-WESLEY MARDEN.

t -v ed a suspension of 

